CROSS Safety Report
Dangerous balcony construction
This report is over 2 years old
During an investigation of a balcony construction, a reporter discovered serious inadequacies related to a total lack of coordination between sub-contract work packages coupled with a lack of appropriate supervision.
Key Learning Outcomes
For principal designers and construction professionals:
Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design
Independent supervision on site by the design team or a third-party inspector can reduce the risk of any unauthorised changes from occurring
The need for collaboration over boundaries should be recognised where multiple parties are involved
The transfer and coordination of relevant information is important to overcome interface issues as demonstrated in this report
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A reporter raises concerns over site supervision and quality control during construction. During an investigation they discovered serious inadequacies related to total lack of co-ordination between sub-contract work packages coupled with lack of appropriate supervision. Invasive investigation and testing showed deliberately masked, very serious structural issues as follows. Concern had been expressed over the 'liveliness' of cantilever balconies but, despite the recent construction date, as-built records could not be located and local authority building regulation submission drawings were incomplete.
Poor coordination leads to alignment issues
Water penetration testing showed leakage through the balcony fixings and random removal of several primary connection bolts showed that there had been alignment problems. The secondary balcony steelwork was supplied and erected by a local fabricator, not the primary steelwork fabricator. Holes in the balcony steelwork did not match with holes in the main steelwork. The site remedy was deliberate machine tapering of Grade 8.8 bolts in primary cantilever connections subject to tension.
Further investigation of a representative sample of numerous balconies indicated that the problem applied throughout. In many instances, the bolt tapering was excessive; so, to rectify further lack of fit, masking tape and building mastic had been utilised to hold bolts in position. In extreme cases of misalignment, bolt heads had been cut off, the threaded section discarded, and the heads tack welded over the bolt holes. Remedial works were carried out.
Several causes identified
In the view of the reporter, the root causes of these issues are:
Principal contractor emphasising 'value engineering' and the client unquestionably accepting that 'value = minimum cost'
Fragmented design input with cost saving achieved by uncoordinated sub-contractor design and detailing with savings further augmented by limiting design team involvement/overall design control. Independent Chartered Structural Engineer involvement was limited
Unreasonable cost and programme constraints and penalties on hard pressed sub-contractors
Expert Panel Comments
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CROSS has had reports about balcony failures over the years as referenced below. There are frequent cases in the public domain from many countries, some constructed from timber, some from reinforced concrete and some from structural steelwork. Balcony failures are usually sudden, without warning, and can result in multiple fatalities. Indeed, just before Christmas 2017 a timber balcony collapsed in Australia causing two deaths and injuries to 17 others.
Similar cases of poor quality construction issues
The integrity of cantilever balconies must be taken very seriously. Usually, it is older balconies that fail so this reported case of balconies in a modern building that might have failed is quite shocking. The core reasons given by the reporter are similar to those given in the Edinburgh Schools Inquiry where a perfect storm of poor communication, poor construction and lack of supervision and inspection contributed to the failure of a masonry panel and repairs to many others.
See the Report of the Independent Inquiry into the Construction of Edinburgh Schools February 2017 and the summarised in the Standing Committee on Structural Safety (SCOSS) alert on Inquiry into the construction of Edinburgh Schools.
Poor quality construction can lead to failures
Another SCOSS alert: Structural stability/integrity of steel frame buildings in their temporary and permanent condition in February 2017 gave as an example the failure of the City Gates Church building where the steel frame collapsed catastrophically. The most likely failure scenario, according to the investigation, was due to poor quality issues during construction.
This type of behaviour on site has been reported to CROSS too often. There are just too many concerns being expressed of inadequate site construction, too many concerns of faults being discovered, and too many concerns of widespread complacency. The report is another which is indicative of a fundamental pattern of danger within the UK construction industry and action must be taken to remedy the situation.
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